Sleep vs Coma vs Anesthesia

The word Coma derives from the ancient Greek word for sleep, but as
applied in modern medical terminology, coma refers to another state
altogether. The comatose person lies unmoving, except for shallow
breathing, indefinitely. People can be in comas for a few hours up to
years. They appear dead to the outside world, except upon close
inspection.

Comas are usually caused by brain injuries or other severe trauma.
They are largely a mystery and people can emerge from comas at times
unforeseen by doctors. Healing can occur during a coma, but it
appears to be a slow process. People in a coma do not demonstrate
sleep signs. They do not move (as people in NREM sleep do), and their
EEG readings are inconsistent with sleep. The person cannot be woken
up, even with powerful stimuli. Doctors use the Glasgow Coma Scale in
their assessment of coma patients. (An alternative is the Rancho Los
Amigos Scale.)

In extreme medical situations, doctor’s use chemicals to induce coma
in patients as part of a treatment strategy. Sometimes coma patients
can actually hear and remember things people say to them when they are
in the coma. Medical intervention is required to maintain life if the coma persist for days;
patients are given nutrition intravenously.

The term vegetative state refers to something else. The person in a
vegetative state is not in a coma. Also called a "coma vigil" or Apallic Syndrome, this state poses ethical dilemmas because patients
do not recover. Their brainstem continues to function, and with
artificial hydration and nutrition they can live indefinitely. They
may even open their eyes and they show a sleep cycle (albeit not a
normal one). But the higher order brain functions are gone. They do
not respond to stimuli and cannot be aroused. There is an effort to
rename this stateUnresponsive Wakefullness Syndrome(http://www.biomedcentral.com/1741-7015/8/68/abstract/)

Anesthesia

Anesthesia reduces the sensation of pain. produces temporary amnesia,
and stops movement of the skeletal muscles. The only stage of sleep
where skeletal muscles are paralyzed is REM, and brain activity
differs substantially between REM and anesthesia.

General anesthesia is when the person is made unconscious. It is so
common that 60,000 surgical patients go under every weekday just in
the United States. The person under anesthesia does not respond -
even the deepest sleep is not as deep (measured by response to
stimuli) as anesthesia.

Colloquiolloy this is called "going to sleep", but it is strictly
speaking not a form of sleep. The doctor may even tell the patient
and his or her family that the surgery will occur while the patient is
asleep, but this is a simplification and the doctor knows it. In a
way, general anesthesia is a reversible coma. EEG readings of brain
activity are not similar to those of any stage of sleep. Indeed,
readings are closer to those of a comatose patient.

Of course anesthesia is not normal sleep and when under anesthesia the person does not experience REM. This is true for most anesthesia drugs used in medical procedures. Subjects accumulate a “REM debt” when under anesthesia and experience rebound REM in the day following. This suggests that there is a REM homeostat the same way there is an overall sleep homeostat (process C in the two-process theory). Some drugs (e.g. isoflurane and sevoflurane ) allow the brain to get its needed NREM sleep, but the anesthesia drug halothane does not. The drug propofol is an exception to the anesthesia rule, as people do not seem to accumulate an REM debt while under its effects, and indeed, sleep debt present upon going under propofol disappear while the anesthesia is in effect.

They make a big deal about risk in hospitals when it comes to
anesthesia. The large majority of patients weather it, but the
reduced heart rate and blood pressure and general metabolism increase
the chances of death. About 1 in a thousand patients wakes up during
anesthesia, leading to sometimes psychologically horrifying
consequences. More scary is when patients do not wake up from
anesthesia on schedule. Some with neurological conditions spend hours
unconscious before waking while the doctors worry. Narcoleptics can
take 8 hours to wake up, while a healthy person takes a few minutes.
Animal experiments suggest that the orexin deficiency associated with
narcolepsy affects waking from anesthesia, not going under.

Even in healthy people, there is an inertia – analogous to sleep
inertia perhaps. Levels of the anesthesia drug must fall to a lower
level for the patient to awaken that it takes to put him or her to
sleep.

Attribute

Sleep

Coma

Anesthesia

Will last less than 12 hours

Yes

No

Yes

Can be induced by drugs

Yes

Yes (in rare medical procedure)

Yes

Person can feel pain

Yes

No

No

Inertia upon awakening

Under 1 hour

Days or weeks

Up to a day

Person awakens in response to sounds or shaking

Yes

No

No

Experienced as refreshing

Yes

No

Not usually

Indicates neurological damage

No (except some hypersomnia)

Yes

No

Surprisingly, doctors have been able to awaken some coma patients by
giving them zolpidem. The mechanism for this phemonemon is not known.
Another of the paradoxes of sleep.